Antibody-mediated immunity and B Cells
The mechanism through which specialized immune cells, primarily B-cell lymphocytes, carry out the IMMUNE RESPONSE to protect the body from extracellular pathogens (disease-causing entities, such as BACTERIA and other microbes, present in the BLOOD or LYMPH that have not invaded the body’s cells). Antibodymediated immunity, also called humoral immunity, encompasses the functions of ANTIBODY production and immune memory. Antibody-mediated immunity functions collaboratively with CELLMEDIATED IMMUNITY to help protect the body from INFECTION.
Specialized B-cell lymphocytes called PLASMA cells produce antibodies, protein molecules that circulate in the blood and lymph. Exposure to antigens for which they are sensitized activates plasma cells to produce antibodies. The antibodies bind with the antigens that match their ANTIGEN receptors (molecular sites that match the configuration of the antigen). The antibody-antigen bond activates the COMPLEMENT CASCADE, a complex interaction of blood proteins (the complement system) that results in penetration and death of the foreign cell.
Antibody binding also releases various CYTOKINES (protein molecules that serve as chemical messengers) that then activate other processes in the immune response. Immune cells that may respond to these messages include macrophages, granulocytes (basophils, eosinophils, and neutrophils), and T-cell lymphocytes (notably helper T-cells [Th2 cells]). The sequence of events takes about 36 hours to unfold after the IMMUNE SYSTEM recognizes the antigen as foreign. The immune response then works to neutralize the threat.
Memory B-cells circulate in the blood and lymph for an extended period of time. They hold a “memory” imprint of specific pathogens. When the PATHOGEN again enters the body, the memory-B cells remember and immediately ramp up antibody production. This process shortcuts the usual immune response, allowing the immune system to mount a defense before the pathogen can initiate an infection.
See also B-CELL LYMPHOCYTE; CELL STRUCTURE AND FUNCTION; GRANULOCYTE; MACROPHAGE; T-CELL LYMPHOCYTE; VACCINE.
